It is my belief that the non-sychro freewheels had big, fat, beefy teeth that wore very well.

With the indexed (hyperglide), the manufacturers started thinning and shaping the cassette teeth (and also new freewheels).

Lately I have had issues with cassettes and new freewheels wearing awfully fast.

It could be different metals. Undoubtedly I am riding a lot. But, I've never had this many problems in the past, and wasn't very proactive with chain replacement.

I do have a dura ace hybrid cassette that I am being very cautious on chain wear and it seems to be lasting pretty well, but it does show some heavy wear.

But, I did manage to toast a new 8 speed freewheel from new to toasted in maybe 1000 miles.